The present invention relates to transmissive display systems and, in particular, to improving contrast ratios or image contrast in such systems.
Transmissive display systems include controllable display cells, such as liquid crystal display cells, that impart image information onto light transmitted from a light source. The light passes through the display cell to an analyzer (e.g., a polarizer) that resolves the light into a display image that is provided at a display output.
As is known in the art, transmissive display systems, such as liquid crystal display systems, commonly suffer from relatively low image contrast. Low image contrast limits image clarity and image quality, particularly at low image brightness. In addition, many transmissive display systems, such as liquid crystal display systems, have conventionally suffered from generally low transmissivity that adversely affects image brightness. With image contrast being generally deemed a fixed characteristic, maximization of image brightness is commonly a primary design goal in transmissive display systems.
However, improvements in light source brightness and display cell transmissivity have somewhat improved overall image brightness. To provide improved image contrast,sa transmissive display system according to the present invention includes a pair of generally non-absorptive, high reflectance, low transmittance optical layers positioned opposite each other across the display cell, such as a liquid crystal display cell. In one implementation, the non-absorptive, high reflectance, low transmittance optical layers may be formed by dielectric coatings on inner surfaces of generally transmissive plates (e.g., polarizers) facing the display cell.
An effect of the non-absorptive, high reflectance, low transmittance optical layers is that successive portions of the originally incident light undergoes multiple reflections or passes between the optical layers. A portion of light is transmitted toward the display output with each reflective pass. While the optical layers reduce the overall transmittance of the display system, the cumulative light transmission from the multiple reflective passes provides a significant increase in image contrast. In some applications, such as professional imaging, medical imaging and publishing, adequate image brightness in combination with significantly improved image contrast provides improved imaging capabilities.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.